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Cystic Fibrosis: Overview

Cystic fibrosis (CF) is a genetic disease that primarily affects the lungs and digestive system of about 30,000 children and adults in the United States (over 60,000 worldwide). The underlying abnormality is the secretion of unusually thick, dehydrated, and sticky mucus in many tissues of the body, including the airways, pancreatic ducts, sweat ducts, sinuses, and bowels.

Obstruction of the pancreatic ducts severely damages the pancreas and results in reduced capacity to make enzymes required to digest proteins and fat. Patients with CF are typically diagnosed in infancy due to symptoms of diarrhea and malnutrition. Later in childhood, obstruction of the small airways of the lung results in the permanent dilation of these bronchi (bronchiectasis), and provides a site where certain infections can take hold. The thick and dehydrated mucous prevents the normal clearance of bacteria and other microbes from the lungs, and patients acquire chronic infections with specific pathogens.

The most important complication of CF is progressive destruction of the lungs, which results in respiratory failure and death in approximately 80% of CF patients. Fortunately, steady advances in medical treatments have provided a range of therapies to slow or prevent the complications of CF, resulting in extended lifespan and improved quality of life for children and adults with CF.

How Common Is Cystic Fibrosis?

There are approximately 30,000 people with CF in the United States, and over 60,000 people worldwide. Moreover, the prevalence of the disease is increasing, with over 1,200 new cases in 2006 from the United States alone (1 out of every 3,500 newborns) [2].

The CFTR mutation is extraordinarily common in the general population, with approximately 10-12 million carriers in the United States. Worldwide, prevalence of the CFTR mutation varies greatly between ethnic groups, with the greatest frequency in European-derived populations and Ashkenazi Jews. Estimates of carrier rates and disease prevalence in the United States are listed in below. In some regions of Europe, an even greater carrier rate has been reported.

Estimated Prevalence of CFTR mutations and new cases ofCystic Fibrosis in the United States

Ethnicity

Carrier rate

Newborns with CF

Caucasian Americans

1 in 29

1 in 3,200

Hispanic Americans

1 in 46

1 in 8,500

African Americans

1 in 65

1 in 17,000

Asian Americans

1 in 90

1 in 31,000

Overall US population

1 in 31

1 in 3500

Many scientists have questioned why the CFTR mutation is so common in select ethnic groups. Geneticists have determined that the important ΔF508 mutation has been present in the human gene pool for over 50,000 years. As the condition has historically been lethal, it is widely assumed that the carrier state (a single CFTR mutation) must have afforded a survival advantage to certain populations. One clue is that ethnic groups with the highest prevalence of the CFTR mutation are indigenous to cooler climates, such as Ireland, parts of Scandinavia, and other European regions. It is known that carriers of CF are predisposed to greater salt loss in their sweat then individuals without the gene. In these climates, salt loss in hot weather would be less relevant, compared to regions of Africa and Asia where the CFTR mutation is very rare.

Proposed diseases that the CF carrier state may protect against include diarrhea from cholera or lactose intolerance, typhoid fever, high blood pressure and tuberculosis. While these theories have not yet been confirmed in man, it seems likely that one (or more) of these mechanisms are responsible for keeping the CFTR mutation in the gene pool.